When a copper layer is deposited on a substrate, such as by electrochemical plating, the copper layer must be deposited on a metal seed layer such as copper which is deposited on the substrate prior to the copper ECP process. As shown in FIG. 1, during an ECP process a contact ring 14 is positioned in close proximity to a wafer 10 as copper is electroplated onto a seed layer 12 which was previously deposited on the wafer 10 prior to the ECP process. The contact ring 14 serves as an electrical conduit between the wafer 10 and an electroplating current source (not shown) and facilitates monitoring of the electrical resistance of the wafer 10 during the ECP process. The electrical resistance of the wafer 10 reveals the presence or absence of the seed layer 12 on the wafer 10.
In the event that the seed layer 12 is insufficiently thin or absent from the wafer 10, copper electroplated onto the wafer 10 has a tendency to peel off of the wafer 10 into the electroplating bath. This contaminates the wafer 10 and subsequent wafers 10 processed in the ECP bath solution. Therefore, the electrical resistance of the wafer 10, as measured through the contact ring 12, serves as a precautionary tool to verify that the seed layer 12 is present on the wafer 10 and of sufficient thickness upon commencement of the ECP process.
However, electrical conductivity of the wafer 10 has been found to be an unreliable indicator as to the thickness characteristics of the seed layer 12 on the wafer 10. Furthermore, seed layer verification can only take place after the wafer 10 is immersed in the electroplating bath solution and electroplating has begun. Therefore, a novel apparatus and method is needed to verify the presence or absence of a seed layer and the thickness of a seed layer on a wafer prior to commencement of an ECP process.